The following references relate to Instrument Landing System Localizers:
1) U.S. Pat. No. 4,415,902; PA1 2) U.S. Pat. No. 4,907,005; and PA1 3) U.S. Pat. No. 4,605,930.
Instrument Landing System (ILS) Localizers provide azimuth guidance to aircraft on final approach to landing. Localizers commonly radiate two superimposed beams. One of these, called "Course" signal, is confined to a relatively narrow angular region on either side of a vertical plane through runway centerline. The other, called "Clearance" signal, typically extends from about .+-.4.degree. to .+-.35.degree. from the same vertical plane. Course and Clearance are radiated on different carrier frequencies in the 108-112 megahertz band. Typically, the two carries differ by about 8 khz. Further details may be found in the references.
Course and Clearance are radiated by a single antenna array in many cases, and transmissions from the array are monitored by an "Integral Monitor" which consists of a recombiner (Ref. 3, e.g.) that sums signals from pickups installed on each antenna of the array to form an analog of the composite Course and Clearance signal radiated at a specific azimuth angle. Zero degrees azimuth and a "width angle" of approximately 2.degree. azimuth are always monitored. In the United States, FAA specifications require separation of the composite signal into its constitutent Course and Clearance components, so that Course and Clearance are separately monitored as if each existed alone. The present invention is a means of precisely achieving the required separation, using a single recombiner, conventional monitor detectors, and a simple, non-critical audio filter. It is simpler, cheaper, and more precise than prior art, which achieves separation by means of networks that form weighted sums of the signals from individual integral monitor pickups, these sums being weighted so that the network output is either all Course signal or all Clearance signal.